This invention relates to apparatus which mixes a polymeric flocculant in dilution water and activates the polymer for liquid/solid separation, as in water and wastewater treatment, and more particularly, to polymer activation and dilution apparatus which produces more rapid and complete activation of the polymer in less processing and aging time than known apparatus, without damaging the polymer structures excessively.
Flocculants and coagulants such as polyelectrolyte materials, polymers, gums and the like ("polymers") are high molecular-weight materials used, among other things, as an aid in removing suspended particles from water, for dewatering sludges, and for other liquid/solid separation applications. The polymers are tightly tangled before activation, and extend or untangle when fully activated in dilution water.
The degree to which a polymer facilitates coagulation and flocculation is improved with greater polymer activation. Polymer activation can perhaps best be measured, for example, by applying an activated polymer to a substrate such as sludge or the like, and measuring the rate of settling under laboratory conditions. The highest rate of settling is indicative of the best possible polymer performance, which is believed to occur when the polymer molecules are at or reasonably close to being fully untangled or activated.
Another indication of the degree of polymer activation is viscosity. Generally, viscosity increases as the polymer becomes untangled or better activated. However, the degree of potential activation is related to the chemical structure of the polymer, the chemical properties of the dilution water in which the polymer is mixed, and the manner in which the polymer is mixed with the dilution water. As a result, a particular polymer may reach a different maximum viscosity in different water solutions or under different mixing conditions. By activating several samples of a particular polymer under varying time and energy conditions, while using a single source of dilution water optimum activation can be determined by measuring and comparing the viscosity of the samples over time. Optimum activation conditions are considered to be those conditions which produce maximum viscosity with the least amount of processing time and aging time (after processing).
The polymer/dilution water solution can be mixed under various energy and time conditions. In commercial applications, it is important that polymers be diluted and activated as quickly and completely as possible, without damaging the polymer molecules. To this end, apparatus which is used for polymer activation and dilution has been refined to more efficiently and more effectively activate the polymer molecules, without destroying them. For example, U.S. Pat. No. 4,522,502 discloses a single stage mixing device which activates polymers very well.
Co-pending patent application Ser. No. 07/657,829, filed Feb. 19, 1991, and patent application Ser. No. 07/370,375, filed Jun. 22, 1989, disclose two-stage mixing apparatus which activate polymers more effectively and efficiently than the single stage mixing device disclosed in U.S. Pat. No. 4,522,502. In the two-stage mixing apparatus, the polymer molecules are subjected to relatively high shear forces for a short period of time in a first processing zone, followed by lower shear forces for a longer period of time in a second processing zone. However, the shear forces are substantially constant within each processing zone. In any event, still further improved activation is desirable.
When activated polymers are used in wastewater treatment plants, the flow volume and composition of the wastewater determines the amount of activated polymer which is needed to properly treat the water. If the character of the wastewater changes, the proportion of polymer in the dilution water, and/or the amount of polymer which is needed, must be adjusted accordingly. Also, changes in the characteristics of the polymer molecules sometimes requires adjustment of the proportion of polymer in the dilution water. For example, the viscosity of many Mannich polymers increases significantly after about 60 days in inventory, which requires the application of higher shear forces and longer residence times in mixing equipment to achieve best performance. A third mixing stage contains elements for a second stage of dilution which provides the flexibility needed to produce optimum hydrodynamic mixing energy and time levels for such circumstances. In the third mixing stage, the polymer processed in the first and second processing zones of two-stage mixing equipment is further diluted with water and processed through a static mixer. The static mixer in the third stage, and the equipment which determines the relative amounts of water and polymer which pass through the static mixer and the two-stage mixing equipment, are known here as post-dilution apparatus.
Known post-dilution equipment is relatively complicated, and often requires several adjustments. In some cases, for example, adjusting the ratio of fresh water which enters the first and second processing zones (pre-dilution) water to fresh water which enters the third processing zone (post-dilution) affects the total volume of water. In other cases, adjusting the pre-dilution water affects the post-dilution water, and vice versa. When this happens, the operator must compensate for the undesired changes, sometimes several times. Thus, there is a need for post-dilution polymer mixing apparatus which is less complicated, and is easier to adjust.
Wastewater treatment facilities are becoming increasingly automated to improve overall performance. However, the relatively complicated nature of the post-dilution systems just described increase the difficulty of automating such facilities. Thus, there is also a need for post-dilution polymer mixing apparatus which is easily adaptable to automation equipment.
Accordingly, one object of this invention is to provide new and improved polymer mixing apparatus.
Another object is to provide new and improved apparatus for diluting and activating polymers in water for use in removing fine particulate matter from wastewater.
Still another object is to provide new and improved polymer activation apparatus with improved activating characteristics.
A still further object is to provide new and improved polymer activation apparatus which is relatively simple in construction, and is readily adaptable to automated control.